7,672 research outputs found
Internal business communications: a three dimensional problem
Communications is a dynamic field -- a company cannot afford to allow its communications program to become static. As an accomplished musician must practice to maintain his skill, so must a company sharpen and refine its communications. Conditions change and the communications program must change to meet the new needs. This will require continuing application of ingenuity and imagination in devising more effective ways of assembling, summarizing and disseminating information to coordinate the functions and activities of the organization
The Geometry and Ionization Structure of the Wind in the Eclipsing Nova-like Variables RW Tri and UX UMa
The UV spectra of nova-like variables are dominated by emission from the
accretion disk, modified by scattering in a wind emanating from the disk. Here
we model the spectra of RW Tri and UX UMa, the only two eclipsing nova-likes
which have been observed with the Hubble Space Telescope in the
far-ultraviolet, in an attempt to constrain the geometry and the ionization
structure of their winds. Using our Monte Carlo radiative transfer code we
computed spectra for simply-parameterized axisymmetric biconical outflow models
and were able to find plausible models for both systems. These reproduce the
primary UV resonance lines - N V, Si IV, and C IV - in the observed spectra in
and out of eclipse. The distribution of these ions in the wind models is
similar in both cases as is the extent of the primary scattering regions in
which these lines are formed. The inferred mass loss rates are 6% to 8% of the
mass accretion rates for the systems. We discuss the implication of our point
models for our understanding of accretion disk winds in cataclysmic variables.Comment: 13 pages, 15 figures and 4 tables. Published in Ap
Characterization of Mmp37p, a \u3cem\u3eSaccharomyces cerevisiae\u3c/em\u3e Mitochondrial Matrix Protein with a Role in Mitochondrial Protein Import
Many mitochondrial proteins are encoded by nuclear genes and after translation in the cytoplasm are imported via translocases in the outer and inner membranes, the TOM and TIM complexes, respectively. Here, we report the characterization of the mitochondrial protein, Mmp37p (YGR046w) and demonstrate its involvement in the process of protein import into mitochondria. Haploid cells deleted of MMP37 are viable but display a temperature-sensitive growth phenotype and are inviable in the absence of mitochondrial DNA. Mmp37p is located in the mitochondrial matrix where it is peripherally associated with the inner membrane. We show that Mmp37p has a role in the translocation of proteins across the mitochondrial inner membrane via the TIM23-PAM complex and further demonstrate that substrates containing a tightly folded domain in close proximity to their mitochondrial targeting sequences display a particular dependency on Mmp37p for mitochondrial import. Prior unfolding of the preprotein, or extension of the region between the targeting signal and the tightly folded domain, relieves their dependency for Mmp37p. Furthermore, evidence is presented to show that Mmp37 may affect the assembly state of the TIM23 complex. On the basis of these findings, we hypothesize that the presence of Mmp37p enhances the early stages of the TIM23 matrix import pathway to ensure engagement of incoming preproteins with the mtHsp70p/PAM complex, a step that is necessary to drive the unfolding and complete translocation of the preprotein into the matrix
The Impact of Accretion Disk Winds on the Optical Spectra of Cataclysmic Variables
Many high-state non-magnetic cataclysmic variables (CVs) exhibit blue-shifted
absorption or P-Cygni profiles associated with ultraviolet (UV) resonance
lines. These features imply the existence of powerful accretion disk winds in
CVs. Here, we use our Monte Carlo ionization and radiative transfer code to
investigate whether disk wind models that produce realistic UV line profiles
are also likely to generate observationally significant recombination line and
continuum emission in the optical waveband. We also test whether outflows may
be responsible for the single-peaked emission line profiles often seen in
high-state CVs and for the weakness of the Balmer absorption edge (relative to
simple models of optically thick accretion disks). We find that a standard disk
wind model that is successful in reproducing the UV spectra of CVs also leaves
a noticeable imprint on the optical spectrum, particularly for systems viewed
at high inclination. The strongest optical wind-formed recombination lines are
H and He II . We demonstrate that a higher-density outflow
model produces all the expected H and He lines and produces a recombination
continuum that can fill in the Balmer jump at high inclinations. This model
displays reasonable verisimilitude with the optical spectrum of RW Trianguli.
No single-peaked emission is seen, although we observe a narrowing of the
double-peaked emission lines from the base of the wind. Finally, we show that
even denser models can produce a single-peaked H line. On the basis of
our results, we suggest that winds can modify, and perhaps even dominate, the
line and continuum emission from CVs.Comment: 15 pages, 13 figures. Accepted to MNRA
Discovery of malathion resistance QTL in Drosophila melanogaster using a bulked phenotyping approach
Drosophila melanogaster has proved an effective system with which to understand the evolutionary genetics and molecular mechanisms of insecticide resistance. Insecticide use has left signatures of selection in the fly genome, and both functional and quantitative genetic studies in the system have identified genes and variants associated with resistance. Here, we use D. melanogaster and leverage a bulk phenotyping and pooled sequencing âextreme quantitative trait lociâ approach to genetically dissect variation in resistance to malathion, an organophosphate insecticide. We resolve 2 quantitative trait loci, one of which implicates allelic variation at the cytochrome P450 gene Cyp6g1, a strong candidate based on previous work. The second shows no overlap with hits from a previous genome-wide association study for malathion resistance, recapitulating other studies showing that different strategies for complex trait dissection in flies can yield apparently different architectures. Notably, we see no genetic signal at the Ace gene. Ace encodes the target of organophosphate insecticide inhibition, and genome-wide association studies have identified strong Ace-linked associations with resistance in flies. The absence of quantitative trait locus implicating Ace here is most likely because our mapping population does not segregate for several of the known functional polymorphisms impacting resistance at Ace, perhaps because our population is derived from flies collected prior to the widespread use of organophosphate insecticides. Our fundamental approach can be an efficient, powerful strategy to dissect genetic variation in resistance traits. Nonetheless, studies seeking to interrogate contemporary insecticide resistance variation may benefit from deriving mapping populations from more recently collected strains
Fine scale structural variants distinguish the genomes of Drosophila melanogaster and D. pseudoobscura
BACKGROUND: A primary objective of comparative genomics is to identify genomic elements of functional significance that contribute to phenotypic diversity. Complex changes in genome structure (insertions, duplications, rearrangements, translocations) may be widespread, and have important effects on organismal diversity. Any survey of genomic variation is incomplete without an assessment of structural changes. RESULTS: We re-examine the genome sequences of the diverged species Drosophila melanogaster and D. pseudoobscura to identify fine-scale structural features that distinguish the genomes. We detect 95 large insertion/deletion events that occur within the introns of orthologous gene pairs, the majority of which represent insertion of transposable elements. We also identify 143 microinversions below 5 kb in size. These microinversions reside within introns or just upstream or downstream of genes, and invert conserved DNA sequence. The sequence conservation within microinversions suggests they may be enriched for functional genetic elements, and their position with respect to known genes implicates them in the regulation of gene expression. Although we found a distinct pattern of GC content across microinversions, this was indistinguishable from the pattern observed across blocks of conserved non-coding sequence. CONCLUSION: Drosophila has long been known as a genus harboring a variety of large inversions that disrupt chromosome colinearity. Here we demonstrate that microinversions, many of which are below 1 kb in length, located in/near genes may also be an important source of genetic variation in Drosophila. Further examination of other Drosophila genome sequences will likely identify an array of novel microinversion events
Line-driven Disk Winds in Active Galactic Nuclei: The Critical Importance of Ionization and Radiative Transfer
Accretion disk winds are thought to produce many of the characteristic
features seen in the spectra of active galactic nuclei (AGN) and quasi-stellar
objects (QSOs). These outflows also represent a natural form of feedback
between the central supermassive black hole and its host galaxy. The mechanism
for driving this mass loss remains unknown, although radiation pressure
mediated by spectral lines is a leading candidate. Here, we calculate the
ionization state of, and emergent spectra for, the hydrodynamic simulation of a
line-driven disk wind previously presented by Proga & Kallman (2004). To
achieve this, we carry out a comprehensive Monte Carlo simulation of the
radiative transfer through, and energy exchange within, the predicted outflow.
We find that the wind is much more ionized than originally estimated. This is
in part because it is much more difficult to shield any wind regions
effectively when the outflow itself is allowed to reprocess and redirect
ionizing photons. As a result, the calculated spectrum that would be observed
from this particular outflow solution would not contain the ultraviolet
spectral lines that are observed in many AGN/QSOs. Furthermore, the wind is so
highly ionized that line-driving would not actually be efficient. This does not
necessarily mean that line-driven winds are not viable. However, our work does
illustrate that in order to arrive at a self-consistent model of line-driven
disk winds in AGN/QSO, it will be critical to include a more detailed treatment
of radiative transfer and ionization in the next generation of hydrodynamic
simulations.Comment: 13 pages, 10 figures - Accepted for publication in Ap
Redox-mediated reactions of vinylferrocene: Toward redox auxiliaries
Chemical redox reactions have been exploited to transform unreactive vinylferrocene into a powerful dienophile for the DielsâAlder reaction and reactive substrate for thiol addition reactions upon conversion to its ferrocenium state. We have further investigated the ability of these reactions to facilitate redox-auxiliary-like reactivity by further hydrogenolyisis of the DielsâAlder adduct to the corresponding cyclopentane derivative
Rearrangement of {α-P2W15} to {PW6} moieties during the assembly of transition-metal-linked polyoxometalate clusters
We report the formation of two polyoxotungstates of the general formula [M6(PW6O26)(α-P2W15O56)2(H2O)2]23â (M = CoII or MnII), which contain {PW6} fragments generated from the [P2W15O56]12â precursor, which demonstrates for the first time the transformation of a Dawson lacunae into a Keggin lacunary building block. Solution analysis of the clusters has been conducted via electrospray ionisation mass spectrometry
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